(1) Field of the Invention
The present invention pertains to a process for removing undesirable surface material from flat materials either in sheet or continuous form, and from narrow tubular material. In particular, the present invention pertains to an apparatus and method for removing scale from the surfaces of processed sheet metal or metal tubing by propelling a scale removing medium, specifically a liquid/particle slurry, against opposite sides of the material passed through the apparatus.
(2) Description of the Related Art
Processed sheet metal is sheet metal that has been prepared for use in making cold rolled sheet metal, and for use in manufacturing some goods. Sheet metal of this type is used in the manufacturing of goods that require a full range of steel thicknesses, for example agricultural equipment, automotive parts, steel containers, and bed frames.
Before sheet metal is used by manufacturers it is typically prepared by a hot rolling process. During the hot rolling process, carbon steel is heated to a temperature in excess of 1,500° F. (815° C.). The heated steel is passed through successive pairs of opposing rollers that reduce the thickness of the steel sheet. Once the hot rolling process is completed, the processed sheet metal or hot rolled steel is reduced in temperature, typically by quenching it in water, oil, or a polymer liquid, all of which are well known in the art. The processed sheet metal is then coiled for convenient storage and transportation to the ultimate user of the processed sheet metal, i.e. the manufacturers of aircraft, automobiles, or home appliances, etc.
During the cooling stages of processing the hot rolled sheet metal, reactions of the sheet metal with oxygen in the air and with the moisture involved in the cooling process can result in the formation of an iron oxide layer, or scale as it is commonly referred to, on the surfaces of the sheet metal. The rate at which the sheet metal is cooled, and the total temperature drop from the hot rolling process effect the amount and composition of the scale that forms on the surface during the cooling process.
In most cases before the sheet metal can be used by the manufacturer, the surface of the sheet metal must be conditioned to provide an appropriate surface for the product being manufactured, so that the sheet metal can be painted or otherwise coated for example. The most common method of removing oxide from the surface of hot rolled or processed sheet metal before coating the sheet metal surfaces is a process known as “pickling.” In this process of removing oxide, the sheet metal, already cooled to ambient temperature following the hot rolling process, is uncoiled and pulled through a bath of acid to chemically remove the scale formed on the sheet metal surfaces. Following removal of the scale by the acid bath, the sheet metal is then washed, dried, and immediately “oiled” to protect the surfaces of the sheet metal from oxidation or rust. The oil provides a film layer barrier to air that shields the bare metal surfaces of the sheet metal from exposure to atmospheric air and moisture. It is critical that the sheet metal be oiled immediately after the pickling process, because the bare metal surfaces will begin to oxidize almost immediately when exposed to the atmospheric air and moisture.
The “pickling” process is effective in removing substantially all of the oxide layer or scale from processed sheet metal. However, the “pickling” process has a number of disadvantages. For example, the acid used in the acid bath of the sheet metal is corrosive; it is damaging to equipment, it is hazardous to people, and is an environmentally hazardous chemical which has special storage and disposal restrictions. In addition, the acid bath stage of the process requires a substantial area in the sheet metal processing facility. Furthermore, “pickling” process lines are frequently slowed down by a phenomena called “black edge” forming on portions of the opposite surfaces of the sheet metal along the edges of the sheet metal being pickled. Black edge is difficult to remove by the pickling process.
Thus, there is a need in the industry for an improved apparatus and method for surface conditioning processed sheet metal by removing oxide or scale from the surfaces of the sheet metal, that does not require the manufacturing floor space of the prior art “pickling” process, and does not require the use of a hazardous chemicals such as the acids.